Nitric oxide delivery devices

ABSTRACT

A gas delivery device includes a nitric oxide generating system. The system has a medium including i) a source of nitrite ions, or ii) a source of nitrite ions and a Cu(II)-ligand complex. A working electrode is in contact with the medium, wherein i) when the medium includes the source of nitrite ions, the working electrode is a copper containing conductive material or a base material coated with a copper containing conductive material, or ii) when the medium includes the source of nitrite ions and the Cu(II)-ligand complex, the working electrode is platinum, gold, carbon, a carbon coated material, and/or mercury. A reference/counter electrode is in contact with the medium and electrically isolated from the working electrode. An inlet conduit is to deliver oxygen gas to the medium, and an outlet conduit is to transport a stream of oxygen gas and nitric oxide from the medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 14/099,942, filed Dec. 7, 2013, which is itself a continuation-in-part application of U.S. Ser. No. 13/852,841, filed Mar. 28, 2013, which itself claims the benefit of U.S. Provisional Application Ser. No. 61/617,886, filed Mar. 30, 2012, each of which is incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under EB000783 and EB004527 awarded by the National Institutes of Health (NIH). The Government has certain rights in the invention.

BACKGROUND

Nitric oxide (NO) has been shown to have several important physiological functions, including its unique vasodilating properties, cancer-fighting potency, anti-platelet activity, and anti-microbial/anti-viral activity. In some instances, NO can be used to control infection, prevent biofilm formation, and minimize inflammation and fibrosis. Although NO is a stable radical, it is highly reactive with hemoglobin and oxygen, thus making delivery of NO to the target site challenging. Stable hydrophilic, as well as hydrophobic NO donors may be employed to take advantage of the potency of NO for a wide range of biomedical applications. NO release polymeric materials and coatings based on diazeniumdiolate chemistry have been used to inhibit platelet adhesion. While these materials and coatings do exhibit NO release, the instability of diazeniumdiolates and other NO donors (e.g., S-nitrosothiols) render the commercialization of these materials and coatings challenging. For example, (Z)-1-[N-methyl-N-[6-(N-methylammoniohexyl)amino]]-diazen-1-ium-1,2-diolate (MAHMA/NO) dispersed in a silicone rubber matrix may, in some instances, prevent thrombus formation on the surface of intravascular sensors. MAHMA/NO may also greatly reduce platelet activity when employed within a polymer coating on the inner walls of extracorporeal circuits. However, MAHMA/NO and its corresponding diamine precursor tend to leach from the surface of the polymer matrix and back react with an oxidative intermediate of NO to form potentially toxic nitrosamines.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

FIG. 1A is a schematic view of an example of a nitric oxide delivery device including a two-electrode configuration;

FIG. 1B is a schematic view of an example of the nitric oxide delivery device including a three-electrode configuration;

FIG. 2A is a schematic view of another example of the nitric oxide delivery device in the form of a single lumen catheter;

FIG. 2B is a schematic, partially cross-sectional view of an example of a nitric oxide delivery triple lumen catheter positioned in a blood vessel;

FIG. 2C is an enlarged, schematic view of the chemical reaction taking place at the working electrode in the catheter of FIG. 2B;

FIG. 2D is a schematic, perspective view of a dual lumen catheter having a dedicated NO generating lumen that houses an example of a medium including a source of nitrite ions and a Cu(II)-ligand complex;

FIG. 3A is a schematic view of another example of the nitric oxide delivery device in the form of a planar patch;

FIG. 3B is an enlarged view of the inside of the planar patch of FIG. 3A;

FIG. 4A is a schematic view of an example of a gas delivery system including a nitric oxide generating system and a blood oxygenator;

FIG. 4B is a schematic view of another example of a gas delivery system including a nitric oxide generating system and an inhalation unit;

FIG. 5A is a graph illustrating the nitric oxide flux from an example of the nitric oxide delivery device over a 24 hour period;

FIG. 5B is an expanded portion of the graph of FIG. 5A;

FIGS. 6A and 6B are graphs illustrating the effect of electrochemical generation of nitric oxide from a catheter surface on biofilm formation for E Coli (FIG. 6A) and A. baumannii (FIG. 6B);

FIG. 7 is a graph illustrating the nitric oxide flux from another example of the nitric oxide delivery device over a 14 hour period with the device being turned on and off at different points;

FIGS. 8A and 8B are graphs illustrating the effect of nitric oxide mediated E. Coli biofilm dispersal in an example of the method using a source of nitrite ions;

FIG. 9 is a graph illustrating the change in potential detected from an example of one type of the catheters disclosed herein, including the potential change after two 2-hour intervals when the catheter was turned on electrochemically to generate nitric oxide gas;

FIGS. 10A and 10B are respective representations of a photograph of an example catheter that electrochemically generated nitric oxide in vivo and of a control catheter that did not electrochemically generate nitric oxide in vivo;

FIG. 11 is a cyclic voltammogram of a bulk solution including 1 mM Cu(II)-tri(2-pyridylmethyl)amine (CuTPMA), a buffer, and varying levels of nitrite;

FIG. 12 is a graph illustrating the modulation of NO generated in a bulk solution (including 4 mM CuTPMA, a buffer, and 100 mM nitrite) by applying −0.2 V, −0.3 V, and −0.4 V (vs. 3 M Ag/AgCl);

FIGS. 13A through 13H are graphs illustrating NO release and flux from a single lumen catheter over 8 days (D1=day 1 . . . D8=day 8) using a cathodic voltage of −0.4 V (vs. 3 M Ag/AgCl), which was periodically turned off to examine the effect on NO generation;

FIG. 14 is a graph illustrating NO release and flux from a single lumen catheter over about 12 hours using varying cathodic voltages;

FIG. 15 is a graph illustrating the effect of NO release from single and dual lumen catheters on thrombus reduction;

FIG. 16A is a finite element analysis illustrating a simulated NO concentration profile near a dual lumen catheter surface (partition coefficient K=S_(silicone)/S_(water)=7, D_(NO) (polymer)>D_(NO) (water));

FIG. 16B is a concentration plot across the line drawn through the dual lumen catheter in FIG. 16A;

FIGS. 17A and 17B are graphs illustrating the effect of nitric oxide mediated E. Coli biofilm dispersal in an example of the method using a medium including a source of nitrite ions and a Cu(II)-ligand complex;

FIG. 18 is a cyclic voltammogram of a bulk solution including 1 mM Cu(II)-tri(2-pyridylmethyl)amine (CuTPMA), a buffer, and varying levels of nitrite and oxygen;

FIG. 19A shows the infrared spectra of N₂O produced using N₂O standards with different levels of N₂O;

FIG. 19B is a calibration curve obtained by integration of the N₂O feature peaks at 2235 cm⁻¹ and 2212 cm⁻¹ in FIG. 19A; and

FIG. 19C shows the infrared spectra of N₂O produced using solutions with a fixed level of CuTPMA and different levels of nitrite.

DETAILED DESCRIPTION

The present disclosure relates generally to nitric oxide delivery devices. In the example devices disclosed herein, the amount of NO that is generated may be controlled in order to have a desired effect in a particular application. As one example, periodic NO generation may be used for killing bacteria in applications where clotting is not an issue (e.g., with urinary catheters). As another example, a steady physiologically-relevant flux of NO for a predetermined time period may be generated to reduce thrombus formation and prevent infection for intravascular catheter applications. As still another example, a steady physiologically-relevant flux of NO for a predetermined time period may be generated in and delivered from a patch attached to the outside of an external wound to assist in wound healing.

Some examples of the nitric oxide delivery device disclosed herein enable one to perform a pulsed electrochemical method within gas permeable polymeric materials to generate and modulate the release of nitric oxide (NO) through the gas permeable polymeric material. These pulsed electrochemical methods may also be used in oxygenators to deliver nitric oxide as well as oxygen to blood during extracorporeal circulation (ECC). In any of these examples, the nitric oxide is electrochemically generated by the reduction of nitrite ions by Cu(I) ions, which are generated at the surface of a working electrode that is made of a copper containing conductive material, or a base material coated with a copper containing conductive material. In some instances, the pulsed electrochemical method is triggered in response to a detected change in potential or pH (e.g., at the surface of a catheter). It has also been found that during NO generation of the pulsed electrochemical method, the working electrode becomes passivated, for example, with an oxide or hydroxide layer, which can inhibit or deleteriously impact the ability to generate of NO. These examples of the method disclosed herein involve a two-step applied potential sequence, where one step generates Cu(I) ions and thus NO, and the other step cleans and refreshes the passivated working electrode surface. The cleaning and refreshing step prepares the working electrode surface for subsequent NO generation.

As used herein, it is to be understood that a “copper containing conductive material” is any material that contains copper and is able to release Cu(I) when an appropriate potential is applied. Examples of these materials include copper or copper alloys. The copper containing conductive material may be in the form of a wire, a mesh, an ink or paint that is applied to a surface (e.g., on an inner surface of the housing), copper nanoparticles that are incorporated/embedded into an electrically conducting polymer matrix or a conductive carbon paste, or any other desirable form. One example of the copper containing conductive material is a copper wire material.

Other examples of the nitric oxide delivery device disclosed herein involve a Cu(II)-ligand complex that functions as a mediator. These examples enable one to perform an electrochemical method that uses a cathodic voltage alone to generate and modulate the release of NO. In these examples, the NO is electrochemically generated by reducing the Cu(II)-ligand complex to a Cu(I)-ligand complex, the Cu(I) of which then functions to reduce nitrite ions (NO₂ ⁻) to NO. The NO that is generated is not bound to the reduced Cu(I) center of the ligand complex, and thus is capable of being transported out of the medium in which is it generated or permeated through to an external environment without performing additional steps to oxidize the ligand complex. The ratio of Cu(I)-ligand complex to Cu(II)-ligand complex at the surface of an inert wire electrode can be controlled by controlling the applied potential. This enables one to control the amount of NO generated for a given concentration of nitrite and Cu(II)-ligand complex. In some instances, the cathodic voltage electrochemical method is triggered in response to a detected change in potential or pH (e.g., at the surface of a catheter).

Any of the examples of the nitric oxide delivery device disclosed herein may be a two electrode or a three electrode system. Some examples of the two electrode system are shown in FIGS. 1A, 2A, 2B, 2D, 3A, 3B, 4A, and 4B; while an example of the three electrode system is shown in FIG. 1B. In the two electrode configurations, a working electrode and a reference or counter electrode (referred to herein as a reference/counter electrode) are used and current passes through the reference/counter electrode. In the three electrode configurations, a working electrode, a reference electrode, and a counter electrode are used. In these systems, the applied voltage is measured versus the reference electrode, but the current passes through the counter electrode. A potentiostat may be used to operate the circuit when either the two or the three electrode system is used.

Referring now to FIGS. 1A and 1B, schemes of electrochemical generation of nitric oxide using the working electrode 12 in a two electrode system 10 and a three electrode system 10′ are respectively depicted. In these example systems 10, 10′, the generated nitric oxide is transferred to a nitric oxide analyzer NOA (e.g., a nitric oxide chemiluminescence analyzer) via an outlet 36 for quantitation of the amount of NO generated. It is to be understood however, that the two and three electrode systems 10, 10′ may not include the outlet 36 and the NOA (see, e.g., FIGS. 4A and 4B). In the examples shown in FIGS. 1A and 1B, the systems 10, 10′ also include a purge gas inlet 32 and an air or N₂ gas inlet 34, which may be used to purge samples (e.g., a source of nitrite ions 26 or a medium 27 including the Cu(II)-ligand complex and the source of nitrite ions) during operation of the systems 10, 10′.

While these systems 10, 10′ may be used to generate NO using any of the methods disclosed herein, it is to be understood that the schemes of electrochemical generation illustrated in FIGS. 1A and 1B may be implemented into other devices, such as catheters (e.g., single lumen catheters shown as reference numeral 100 in FIG. 2A and multi-lumen catheters shown as reference numeral 100′ in FIG. 2B and 100″ in FIG. 2D), patches (shown as reference numeral 200 in FIG. 3A), and gas delivery systems (shown as reference numeral 300 in FIG. 4A and 300′ in FIG. 4B). Rather than transferring the NO to the NO analyzer for quantitation, these devices 100, 100′, 100″, 200, 300, and 300′ either release the generated NO into the external/surrounding environment through the walls of the catheter tubing or through the planar patch material, or transport the generated NO in a gas stream to a blood oxygenator (FIG. 4A) or an inhalation unit (FIG. 4B). In some these devices, the external environment may be exposed to or may contain blood. In reference to FIGS. 1A and 1B, the schemes of electrochemical generation will be described, and in reference to FIGS. 2A through 4B, various examples of the devices incorporating examples of these schemes will be described.

Referring now to FIG. 1A, the two electrode system 10 includes the working electrode 12 and the reference/counter electrode 14. In the examples of the method in which the source of nitrite ions 26 is used, the working electrode 12 may be an electrode made of the copper containing conductive material or another electrode (e.g., platinum, gold, carbon, mercury, etc.) coated with the copper containing conductive material. In the examples of the method in which the medium 27 is used, the working electrode 12 may be an electrode made of platinum, gold, carbon (e.g., glassy carbon) or a carbon coated material, mercury, etc. In any examples of the method disclosed herein, the reference/counter electrode 14 may be silver/silver chloride or some other reference electrode or pseudo reference electrode.

Conductive leads 16, 18 are respectively and electrically connected to the working electrode 12 and the reference/counter electrode 14. The conductive leads 16, 18 electrically connect the respective electrodes 12, 14 to the electronics 20 (e.g., a potentiostat) that are used to control the applied voltage, and in some instances, record potential shift changes and compare potential shift changes to a preset threshold value. Conductive leads 16, 18 may be made of any conductive material, examples of which include copper wires, platinum wires, stainless steel wires, aluminum wires, etc.

The working electrode 12 in FIG. 1A is shown in a glass tube 22, which is configured so that an end 24 of the working electrode 12 is exposed to the source of nitrite ions 26 or the medium 27, but the source of nitrite ions 26 or medium 27 does not enter the tube 22. The reference/counter electrode 14 may also be contained within a glass tube 22′. The tube 22′ is configured so that an end 25 of the reference/counter electrode 14 is exposed to the source of nitrite ions 26 or to the medium 27, but the source of nitrite ions 26 or medium 27 does not enter the tube 22′.

In an example, the source of nitrite ions 26 may be a water soluble, inorganic nitrite salt in an aqueous solution or within a hydrogel (e.g., hydroxymethylcellulose, poly(vinyl alcohol) (PVA), gelatin, etc.). Some examples of water soluble, inorganic nitrite salts include alkali metal and alkaline earth metal nitrite salts. Specific examples include nitrite salts of Li, Na, K, Rb, Ca, and Mg. Most other metal salts are also soluble in water, for example, Al salts and Fe salts. One specific example of the source of nitrite 26 is NaNO₂.

In another example, the source of nitrite ions 26 may be a lipophilic quaternary ammonium nitrite species soluble in an organic polymeric phase. This particular source of nitrite ions 26 may not be suitable for the examples of the catheter disclosed herein that have a modified wall/exterior surface. For the other examples that may include the lipophilic quaternary ammonium nitrite species, the lipophilic quaternary ammonium nitrite salt may be chosen from tetradodecylammonium nitrite, tridodecylmethylammonium nitrite, tetradecylammonium nitrite, and tetraoctylammonium nitrite. The organic polymeric phase may be chosen from polyurethane, poly(vinyl chloride), polymethacrylate, and polydimethylsiloxane (PDMS). The organic polymeric phase may be doped with a relatively high concentration of the lipophilic quaternary ammonium nitrite salt. The high concentration of the lipophilic quaternary ammonium nitrite salt will depend, at least in part, on the polymer matrix used. In an example, the high concentration ranges from about 1 mM to about 300 mM. In one example when the lipophilic quaternary ammonium nitrite species is used as the source of nitrite ions 26, the working electrode 12 (i.e., the source of Cu(I)) may be nanoparticles of the copper containing conductive material embedded in the organic polymer phase.

In examples that utilize the medium 27, any of the previously described water soluble, inorganic nitrite salts in aqueous solution or within the hydrogel may be used as the source of nitrite ions. In addition, the medium 27 includes the Cu(II)-ligand complex, which is water soluble. Examples of the Cu(II)-ligand complex include Cu(II)-tri(2-pyridylmethyl)amine (CuTPMA), Cu(II)-tri(2-dimethylamino)ethyl]amine (CuMe₆Tren), Cu(II)-tri(2-pyridylmethyl)phosphine (CuTPMP), and combinations thereof. These structures are shown below:

While some examples of the Cu(II)-ligand complex are provided herein, it is to be understood that other water soluble Cu(II)-complexes may be used.

The source of nitrite ions 26 or the medium 27 may also include a buffer and/or another additive that aids in driving the reduction reaction of Cu(I) with nitrite. Examples of suitable buffers are phosphate buffered saline (PBS) or 3-(N-morpholino)propanesulfonic acid (MOPS).

An example of the other suitable additive is ethylenediaminetetraacetic acid (EDTA). EDTA helps drive the reduction reaction of Cu(I) with nitrite (Cu(I)+NO₂ ⁻+2H⁺→Cu(II)+NO+H₂O) to the product side by chelating with Cu(II) stronger than with Cu(I). As an example, the source of nitrite ions 26 includes 1 M NaNO₂, 25 mM EDTA and 0.138 M NaCl in 1 M PBS (pH 7.2). As another example, the medium 27 includes 4 mM CuTPMA, 0.4 M NaNO₂, and 0.2 M NaCl in 0.5 M MOPS buffer (pH 7.2). When a Ag/AgCl reference is utilized, a fixed level of chloride ions is provided (e.g., as NaCl) in the source of nitrite ions 26 or the medium 27 so that the reference electrode can maintain a constant potential (EMF).

Electrochemical generation of nitric oxide using the two electrode system 10 of FIG. 1A involves application of voltage (e.g., continuously or as pulses) to the working electrode 12, where current passes through the reference/counter electrode 14.

In examples using the source of nitrite ions 26 (i.e., not the medium 27 including the Cu(II)-ligand complex), a cathodic voltage pulse is applied to the working electrode 12 to clean the surface (including the end 24) of the working electrode 12. In these examples, the cathodic pulse may be applied for a period of time that is suitable for refreshing the working electrode 12 surface. In an example, the time for which the cathodic pulse is applied to refresh the working electrode 12 ranges from about 1 second to about 10 minutes. In these examples, an anodic voltage pulse is then applied to the working electrode 12. The anodic voltage pulse produces a low concentration of Cu(I) ions at the electrode 12 surface. The Cu(I) ions produced at the end 24 react directly with nitrite in the source of nitrite ions 26 to generate nitric oxide gas. The anodic voltage pulse is applied to the working electrode 12 for a limited time interval ranging from about 1 second to about 10 minutes, at least in part because Cu₂O/CuOH forms on the electrode 12 when the anodic voltage pulse is applied. The oxide formed on the surface of the working electrode 12 in these examples of the method interferes with the generation of nitric oxide gas. When it is desired to generate NO again, the cathodic pulse is applied to clean the electrode 12, and then the anodic pulse is applied to generate NO. To observe consistent reduction of nitrite to NO in these examples of the method, the two-step potential sequence (i.e., cathodic pulse followed by anodic pulse) is continuously and repeatedly applied to the working electrode 12.

It is to be understood that the time frames provided for application of the cathodic voltage pulse and the anodic voltage pulse are examples and may be varied depending upon the amount of NO to be generated and/or the time needed to refresh the working electrode 12 surface. Generally, if less Cu(I) is generated during the anodic step, than the cathodic step will be shorter because less time is needed to refresh the working electrode surface. As an example, it is believed that a cycle that includes a 5 second cathodic pulse and a 5 second anodic pulse may be used. In this example, the NO production may be relatively low due, at least in part, to rapid depletion of nitrite near the working electrode 12. Nitrite arrives at the electrode 12 surface by diffusion, and the rate of NO production may be faster than the rate of nitrite diffusion. However, such low levels of NO may be desirable in some instances.

In examples using the medium 27 including both the source of nitrite ions and the Cu(II)-ligand complex, a cathodic voltage is applied to the working electrode 12. The cathodic voltage may be applied continuously, in pulses (e.g., more negative voltage followed by less negative voltage), or using a desirable on/off sequence. When applied, the cathodic voltage pulse produces a low concentration of the Cu(I)-ligand complex at the electrode 12 surface. The Cu(I)-ligand complex produced at the end 24 reacts directly with nitrite in the medium 27 to generate nitric oxide gas. The cathodic voltage may be applied to the working electrode 12 for any time interval up to, for example, 30 days. In some instances, it is believed that the voltage may be applied continuously for even longer than 30 days. When it is desired to stop generating NO, the cathodic voltage is no longer applied to the electrode 12. In some examples, the cathodic voltage may be turned on periodically (e.g., for 1 to 3 hours per day to kill bacteria), and the usable life of the device may be for multiple months. In other examples, when the voltage is continuously applied, the voltage may be modulated to be more or less negative in order to increase or decrease, respectively, the rate of NO production, and thus the flux of NO emitted from the surfaces of the device (e.g., catheter, wound healing patch, etc.). In some example, a more negative voltage may be applied for a shorter time than a less negative voltage in order to conserve the nitrite source in the solution 27 for a longer period. Variations on the application of the cathodic voltage in this example of the method are also contemplated as being within the purview of this disclosure.

Referring now to FIG. 1B, the three electrode system 10′ includes the working electrode 12, the reference electrode 28, and the counter electrode 30. Similar to the two electrode system 10, the working electrode 12 that is used with the source of nitrite ions 26 may be an electrode made of the copper containing conductive material or another electrode (e.g., platinum, gold, carbon, mercury, etc.) coated with the copper containing conductive material, and the working electrode 12 that is used with the medium 27 may be an electrode made of platinum, gold, carbon (e.g., glassy carbon) or a carbon coated material, mercury, etc. In an example of the three electrode system 10′, the reference electrode 28 is silver/silver chloride and the counter electrode 30 is platinum (e.g., a platinum mesh). In the three electrode system 10′, the reference electrode 28 may also be an ion-selective pseudo-reference electrode (e.g., a sodium-selective electrode or a potassium-selective electrode).

Conductive leads 16, 18 are respectively and electrically connected to the working electrode 12 and the counter electrode 30. A conductive lead 38 electrically connects the reference electrode 28 to the working and counter electrodes 12, 30. The conductive leads 16, 18, 38 electrically connect the respective electrodes 12, 30, 28 to the electronics 20 (e.g., a potentiostat) that are used to control the applied voltages, and in some instances, record potential shift changes and compare potential shift changes to a preset threshold value. The conductive leads 16, 18, 38 may be made of any of the conductive materials previously described.

In FIG. 1B, the working electrode 12 is set up in a similar manner to that described in reference to FIG. 1A. Also in FIG. 1B, the counter electrode 30 is set up in a similar manner to that described for the reference/counter electrode 14 in reference to FIG. 1A. The counter electrode 30 used in the three electrode system 10′ may be inserted into the source of nitrite ions 26 or the medium 27. Electrochemical generation of nitric oxide using the three electrode system 10′ of FIG. 1B involves application of voltage (e.g., continuously or as pulses) to the working electrode 12, where current passes through the counter electrode 30. The voltage applied to the working electrode 12 and through the counter electrode 30 is measured against the reference electrode 28. This system 10′ may be used to apply the previously described two-step potential sequence (i.e., cathodic pulse followed by anodic pulse) to the working electrode 12 in the presence of the source of nitrite ions 26 to generate NO, or may be used to apply the previously described cathodic potential to the electrode 12 in the presence of the medium 27 to generate NO.

Some of the components of the systems 10, 10′ of FIGS. 1A and 1B may be incorporated into medical devices, such as catheters 100 (shown in FIG. 2A), 100′ (shown in FIG. 2B), or 100″ (shown in FIG. 2D), or planar patches 200 (shown in FIGS. 3A and 3B), or gas delivery devices 300 (shown in FIG. 4A) or 300′ (shown in FIG. 4B). These devices 100, 100′, 100″, 200, 300, 300′ may be operated to selectively generate NO as described above. In some examples, the catheters 100, 100′, 100″ may be configured to detect the presence of bacteria (e.g., biofilm) on its surface, and in response, turn on the electrochemical cell to generate NO to disperse the attached bacteria and keep the surface free of bacteria. As will be described further below, in these examples, the housing 40 of the catheter 100, 100′, 100″ is ion conductive so that the surface potential of the housing 40 can be measured and an external reference electrode is utilized.

In the devices 100, 100′, 100″, 200, 300, 300′, the electronics that apply the desired potentials, and in some instances record and compare potential shifts and values, may be minimized to be secured to the nitric oxide permeable material (e.g., housing 40) or to the nitric oxide generating system (shown in FIGS. 4A and 4B), and may be operated via a battery or another source of energy (e.g., solar generator, an energy harvesting device, etc.). Furthermore, while the following description relates to examples of the two electrode system, it is to be understood that the three electrode system may also be implemented into the medical devices.

Referring now to FIG. 2A, the single lumen catheter 100 illustrated is a two electrode system (similar to system 10) that includes a housing 40 that is permeable to nitric oxide. It is to be understood that the single lumen catheter 100 may be particularly desirable for applications that do not require blood sampling, drug and/or nutrient infusion, etc. For example, the single lumen catheter 100 may be particularly suitable for studies demonstrating the effectiveness of the electrochemical NO generating methods disclosed herein. For many medical applications however, blood sampling and/or drug and/or nutrient infusion is desirable, and thus the multi-lumen catheters 100′, 100″ described hereinbelow may be more desirable for those types of applications.

Still referring to FIG. 2A, the housing 40 keeps the source of nitrite ions 26 or the medium 27 and the electrodes 12, 14 separated from the external environment. The housing material is selected so as to prevent the source of nitrite ions 26 or the medium 27 from leaking out of the housing 40 while allowing NO gas to permeate through the housing 40 to the external environment. Examples of suitable materials for the housing 40 include silicone rubber, biomedical grade polyurethane, polytetrafluoroethylene (PTFE), polytetrafluoroethylene derivatives (e.g., ethylene tetrafluoroethylene (ETFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy (PFA), etc.), polymethacrylate, and poly(vinyl chloride). The housing 40 used in the catheter 100 may have a cylindrical geometry.

Both the working electrode 12 and the reference/counter electrode 14 are positioned within the housing 40. The electrodes 12, 14 are positioned such that they are electrically isolated from one another. The exposed electrodes 12, 14 may be physically separated from one another. As shown in FIG. 2A, in an example, a portion of the reference/counter electrode 14 that is adjacent to the working electrode 12 within the housing 40 may be coated with an insulating layer 42 in order to ensure electrical isolation of the two electrodes 12, 14. This insulating layer 42 is described further hereinbelow.

Conductive leads 16, 18 are electrically connected to the respective electrodes 12, 14. The leads 16, 18 may be part of the respective electrodes 12, 14, or may be separate wires that are electrically connected to the respective electrodes 12, 14. The leads 16, 18 extend from the electrodes 12, 14 (which are inside the housing 40) to electronics (not shown) which are outside of the housing 40. FIG. 2A illustrates an example in which the leads 16, 18 are part of the respective electrodes 12, 14. In this example, the working electrode 12 includes the coiled portion within the housing 40, and the lead portion 16 extending outside of the housing 40. Also in this example, the reference/counter electrode 14 includes the coiled portion within the housing 40, and the lead portion 18 that is partially inside of the housing and partially outside of the housing 40. In examples in which the leads 16, 18 are separate wires that are connected to the electrodes 12, 14, it is to be understood that the leads 16, 18 may be the same material as, or different materials than the electrodes 12, 14.

The housing 40 may be sealed at areas where the leads 16, 18 pass therethrough. In an example, the housing 40 is sealed using a silicone rubber seal/sealant (an example of which shown in FIG. 2B as reference numeral 43).

The housing 40 also contains the source of nitrite ions 26 or the medium 27. Any of the sources 26 or media 27 previously described may be used in this example device 100. The source of nitrite ions 26 or the medium 27 is contained within the housing 40 such that the working electrode 12 and the reference/counter electrode 14 are in contact with the source of nitrite ions 26 or the medium 27.

While not shown in FIG. 2A, it is to be understood that when the source of nitrite ions 26 is used, the working electrode 12 may be formed of an ink or paint that includes the copper containing conductive material, and the reference/counter electrode 14 may be formed of an ink or paint that includes silver or another suitable conductive material. In this example, the electrodes 12, 14 may be screen printed or otherwise formed on the inner walls of the housing 40.

As briefly mentioned above, areas or portions of one or more of the electrodes 12, 14 and/or the leads 16, 18 may be coated with an insulating layer 42. As illustrated in FIG. 2A, a portion of the reference/counter electrode 14 that is adjacent to the working electrode 12 within the housing 40 may be coated with the insulating layer 42. In this example, at least a portion of the reference/counter electrode 14 within the housing 40 (e.g., the coiled portion shown in FIG. 2A) remains exposed. Also as illustrated in FIG. 2A, the leads 16, 18 may be coated with the insulating layer 42. In these examples, ends of the leads 16, 18 may remain exposed to electrically connect to suitable electronics. Any insulating material may be used for the insulating layer 42, examples of which include polytetrafluoroethylene (PTFE), polyethylene, silicone, etc. In other examples, the electrodes 12, 14 and/or the leads 16, 18 may remain uncoated.

Electrochemical generation of nitric oxide using the catheter 100 of FIG. 2A and the source of nitrite ions 26 involves application of a cathodic voltage pulse to the working electrode 12 to clean the surface of the working electrode 12, and then application of an anodic voltage pulse to the working electrode 12 to produce a concentration of Cu(I) ions at the electrode 12 surface. The Cu(I) ions produced at the surface react directly with nitrite in the source of nitrite ions 26 to generate nitric oxide gas, which permeates through the housing 40 to the external environment.

Electrochemical generation of nitric oxide using the catheter 100 of FIG. 2A and the medium 27 involves application of a cathodic voltage to the working electrode 12 to produce a concentration of Cu(I)-ligand complex in the medium 27, which react directly with nitrite in the medium 27 to generate nitric oxide gas, which permeates through the housing 40 to the external environment.

As previously mentioned, in either examples of the method disclosed herein, the potential applied to the working electrode 12 may be controlled to turn NO release on or off. An advantage of this control is that nitrite salts may be dissolved in high concentrations and incorporated into reservoirs in the lumen of the catheter 100. As an example involving a dual lumen biomedical catheter, one lumen may be used as a nitrite salt reservoir, and the second lumen may be used to sample blood, infuse therapeutic agents, etc. It is believed that a 150 μm thick layer of a 1 M nitrite solution can produce a 1×10⁻¹⁰ mol·min⁻¹·cm⁻² NO flux continuously for at least 100 days in a cylindrical arrangement (e.g., a catheter) or planar arrangement (e.g., the patch described below).

It has been found (see Example 15) that using high concentrations of the nitrite salts in the source 26 or the medium 27 significantly reduces the amount of N₂O that may be generated during the electrochemical methods disclosed herein. In the examples disclosed herein, at least 100 mM nitrite is used as the source of nitrite ions 26 or in the medium 27, and amounts lower than 100 mM cannot be used. These levels of nitrite suppress the formation of N₂O to negligible levels. As an example, a source of nitrite ions 26 or a medium 27 including 400 mM nitrite may result in less than 5% N₂O in the total gas species that is generated using the methods disclosed herein. It is believed that the excess nitrite competitively binds to the Cu center of the ligand complex (after the mediated reduction of nitrite to NO by the complex) so that the electrogenerated NO leaves the copper-ligand complex, rather than such a complex being reduced electrochemically again in the presence of another nitrite ion to form N₂O. This prevents the formation of significant levels of N₂O.

It is to be understood that while illustrated as a single lumen catheter configuration in FIG. 2A, in other examples (e.g., when to be used in clinical practice and other medical applications), the electrochemical generating concepts disclosed herein may be implemented using a multi-lumen catheter. The multi-lumen catheter 100′ (FIG. 2B) or 100″ (FIG. 2D) may include two or more lumens (three, four, etc.), as long as one of the lumens is dedicated for NO generation. The dedicated NO generating lumen of the multi-lumen catheters may be configured for performing any of the methods disclosed herein. One example of the dedicated NO generating lumen of the multi-lumen catheter may include the medium 27 and the electrodes 12, 14, and the application of a cathodic pulse may generate NO. Another example of the dedicated NO generating lumen of the multi-lumen catheter may include the source of nitrite ions 26 and the electrodes 12, 14, and the application of the two-step potential sequence (i.e., cathodic pulse followed by anodic pulse) may clean the electrode 12 and generate NO.

An example of a multi-lumen catheter 100″ having at least one lumen L₁ dedicated for NO generation is depicted in FIG. 2D. While this example is shown with the medium 27, it is to be understood that the electrodes 12, 14 may be selected to be used with the source of nitrite ions 26 and the pulsed electrochemical method disclosed herein.

In the example of FIG. 2D, the lumen L₁ includes the working electrode 12 and the reference/counter electrode 14 so that at least some of the electrode 12, 14 is in contact with the medium 27 contained within the lumen L₁. While not shown, it is to be understood that the lumen L₁ may also be sealed, for example, with a silicone rubber cap.

Within the lumen L₁, when a cathodic voltage is applied (e.g., −0.4 V vs. reference electrode 14), the Cu(II)-ligand complex in the medium 27 is reduced to the Cu(I)-ligand complex. The Cu(I)-ligand complex reacts directly with nitrite in the solution 27 to generate nitric oxide gas, which permeates through the housing 40 to the external environment. The reactions (i.e., (Cu(II)-ligand complex→Cu(I)-ligand complex and Cu(I)-ligand complex+NO₂ ⁻+2H⁺→Cu(II)-ligand complex+NO+H₂O) taking place within the solution are shown in FIG. 2D.

In the multi-lumen catheter 100″ example, there is at least one open lumen L₂ in addition to the lumen L₁ dedicated for NO generation. Blood can be removed through the open lumen L₂ of the catheter 100″, or therapeutic solutions can be infused into a patient through the open lumen(s) L₂.

In any of the catheter 100, 100′, 100″ examples disclosed herein, the wall, and thus the exterior surface S, of the housing 40 may be modified to detect any charged species (e.g., negatively charged or positively charged bacteria) that is sitting on the exterior surface S. Bacteria, and in particular biofilm, that forms on the exterior surface S of the catheter 100, 100′, 100″ may contribute to catheter related infections. The catheter 100, 100′, 100″ having the modified surface can detect the bacteria, and in response, can initiate NO generation from within the housing 40. The catheter 100, 100′, 100″ can release NO that is generated by the electrochemical methods disclosed herein. The released NO acts as an effective antimicrobial and biofilm dispersal agent. The released NO may also exhibit potent antithrombotic activity.

The wall and exterior surface S of the housing 40 may be modified with any additive(s) that will render the surface S with the ability to detect charge on the surface S. In an example, the additive(s) are impregnated into the exterior surface S. It is to be understood that any of the housing materials mentioned herein may be modified with a cation/anionic salt and a plasticizer. Examples of the cation/anionic salt include tetradodecylammonium tetrakis (4-chlorophenyl) borate, tridodecylmethylammonium tetrakis (bis-trifluormethylphenyl borate), etc. Examples of the plasticizer include dibutyl sebacate, dioctyl sebacate, nitrophenyloctyl ether, etc. In an example, silicone tubing is impregnated with tetradodecylammonium tetrakis (4-chlorophenyl) borate and dioctyl sebacate in an m-xylene solution.

In an example, the modified exterior surface S is capable of detecting charged species that are in contact with the surface S by measuring the voltage between the inner solution/hydrogel and the outer contact phase (e.g., the blood, using an external reference electrode). The electronics operatively connected to the catheter 100, 100′, 100″ are able to record negative and positive potential shifts, which depend upon the number of bacteria on the surface S of the catheter 100, 100′, 100″. The potential shifts are measured from an initial operating potential of the catheter 100, 100′, 100″ (i.e., a background potential). In general, more bacteria present on the surface S results in a greater negative or positive potential shift from the background potential. Storage/memory associated with the electronics may be programmed with a threshold value of potential shift. The threshold value of potential shift may be based upon an undesired number of bacteria present on the surface S. For example, it may be determined that a 100 mV shift in potential is an indication of a critical mass of bacteria on the surface S, and this value may be stored as the threshold value to which recorded values are compared. When the amount of bacteria present on the surface S reaches the undesired number, the recorded potential shift will exceed the threshold value. In an example, the potential shifts are recorded by a high impedance voltmeter.

The electronics (which may include a controller running computer readable code stored on a non-transitory, computer readable medium) are also configured to recognize that the threshold value of potential shift has been reached or exceeded, and in response, will automatically trigger electrochemical NO production. In other words, upon recognizing that the recorded potential shift meets or exceeds the threshold value, the electronics will initiate the electrochemical pulse method disclosed herein (when the source of nitrite ions 26 is used) or the constant cathodic voltage electrochemical method disclosed herein (when the medium 27 is used).

In an example in which the source of nitrite ions 26 is used, the electronics are configured to first apply a cathodic voltage pulse to the working electrode 12 to clean the surface of the electrode 12, and then apply an anodic voltage pulse to the working electrode 12 to produce a low concentration of Cu(I) ions at the working electrode 12 surface. The Cu(I) ions produced at the surface react directly with nitrite in the source of nitrite ions 26 to generate nitric oxide gas, which permeates through the housing 40 to the external environment. The released NO disperses the bacteria on the surface S. As a result of bacteria dispersal, the surface potential shifts back to the background value at which the catheter 100, 100′, 100″ was operating initially. Upon recognizing that that background potential is again reached, the electronics are configured to turn off NO generation (i.e., stop the electrochemical pulse method). The catheter 100, 100′, 100″ then operates at the background potential until the accumulation of bacteria on the surface S is enough to cause another potential shift.

In an example in which the medium 27 is used, the electronics are configured to first apply a cathodic voltage to the working electrode 12 to reduce the Cu(II)-ligand complex to produce a low concentration of Cu(I)-ligand complex. The Cu(I)-ligand complex then reacts directly with nitrite in the medium 27 to generate nitric oxide gas, which permeates through the housing 40 to the external environment. The released NO disperses the bacteria on the surface S. As a result of bacteria dispersal, the surface potential shifts back to the background value at which the catheter 100, 100′, 100″ was operating initially. Upon recognizing that that background potential is again reached, the electronics are configured to turn off NO generation (i.e., stop the application of the cathodic voltage). The catheter 100 or 100′ then operates at the background potential until the accumulation of bacteria on the surface S is enough to cause another potential shift.

FIG. 2B schematically illustrates an example of a triple lumen catheter 100′ positioned within a blood vessel 44 (also showing red blood cells 46). In this example, lumens L₁ and L₃ are open lumens used for sampling blood and/or infusing therapeutic agents (represented by the vertical arrows at the open ends of the lumens L₁ and L₃. Lumen L₂ is the dedicated NO generating lumen. In this example, the lumen L₂ includes the source of nitrite ions 26 and the electrode 12 made of or coated with the copper containing conductive material. It is to be understood the lumen L₂ may also be configured with the medium 27 and its associated electrode 12. While not shown in FIG. 2B, this example could also include an external reference electrode that would be in contact with the sample phase (e.g., the blood in the blood vessel 44), if detection of adhered bacteria 48 on the surface S of the device 100′ via either a surface charge effect or local pH change were desired to signal the initiation of electrochemical NO release.

In this example, bacteria 48 on the surface S has been detected and a potential shift resulting from the bacteria 48 has been recognized as exceeding the pre-programmed threshold value. As such, electrochemical pulses have been initiated using electrodes 12, 14, and NO is generated. The reaction (i.e., (Cu(I)+NO₂ ⁻+2H⁺→Cu(II)+NO+H₂O) taking place at the working electrode 12 is shown in FIG. 2C. The generated NO permeates through the housing 40 into the surrounding environment, where it contributes to the prevention of smooth muscle cell proliferation, the prevention of platelet activaton/thrombosis, and kills bacteria 48.

In still another example, the housing 40 may be modified to detect localized pH changes at the exterior surface S. The housing wall and exterior surface S may be doped with a chemical (e.g., a pH sensitive material) that allows electrochemical detection of the pH changes. In an example, the housing 40 can be doped with any proton ionophore, such as tridodecylamine (TDDA), along with from about 10 mol % to about 50 mol % (relative to the ionophore) of any tetraphenylborate species (lipophilic anion site).

The pH sensitive catheter may be operated in combination with the previously mentioned reference electrode external to the housing 40. The external reference electrode facilitates monitoring of the potential across the pH sensitive housing 40, where the potential is a function of the pH of the external environment (including bacteria or other cells adhering to the external surface S) being monitored. As such, the potential between the reference/counter electrode 14 and the external reference electrode tracks the pH of the external environment. In an example, a potential change due to any difference in proton activity at the exterior surface S of the housing 40 (measured using the external reference electrode in contact with a solution outside of the housing 40) versus proton activity at the inner surface e (i.e., pH buffer in the source of nitrite ions 26 or the medium 27, measured using reference/counter electrode 14) may be detected using a high impedance voltmeter. This potential change indicates the presence of bacteria or other cells adhering to the exterior surface S of the catheter housing 40. A given pH change as determined from the measured potential will then trigger the electrochemical NO generation process, as described above when using surface charge to detect the presence of cells.

Referring now to FIGS. 3A and 3B, the planar patch 200 and an exploded view of its interior are respectively depicted. The planar patch 200 illustrated is a two electrode system (similar to system 10) that includes the housing 40 that is permeable to nitric oxide. The housing 40 of the planar patch 200 functions in the same manner as the housing 40 used for the catheter 100, 100′. 100″. In this example however, the housing 40 has the shape of a relatively flat cube, relatively flat rectangular box, or other relatively flat three-dimensional shape. The housing 40 does have a length, width, and a depth; however the depth may be relatively small so that the planar patch 200 is flexible and able to conform to the shape of a desired subject (e.g., a limb, appendage, etc. that the planar patch is affixed, adhered, or otherwise secured to). The planar patch 200 may also be constructed so that only the surface that is to be adjacent to the desired subject is made of the permeable material, while the remainder of the surfaces is impermeable to NO. In this example then, NO is releasable from the desired surface alone.

In this example, the working electrode 12 is a mesh 12′, which may be a network of wires or screen printed lines. The material of the working electrode 12, 12′ may vary depending upon whether the source of nitrite ions 26 or the solution 27 is used. Similarly, the reference/counter electrode 14 is a metal-containing mesh 14′, which may be a network of metal (Pt) or other conductive material (Ag/AgCl) wires or screen printed lines. In an example of the planar patch 200 in which the source of nitrite ions 26 is used, the working electrode 12 may also be formed of nanoparticles of the copper containing conductive material dissolved in a suitable polymer matrix.

The meshes 12′, 14′ (or, in an example, the mesh 14′ and the polymer matrix containing copper containing nanoparticles) are electrically isolated from one another by a separator 44. Examples of suitable separators 44 include polymeric materials, such as polyethylene, polypropylene, polytetrafluoroethylene, poly(vinyl chloride), or other like materials. While the separator 44 is electrically insulating, it is also capable of conducting ions (i.e., is ionically conducting).

Conductive leads 16, 18 are electrically connected to the respective electrode meshes 12′, 14′. In this example, the leads are separate wires that are electrically connected to the respective meshes 12′, 14′. The leads 16, 18 extend from the meshes 12′, 14′ (which are inside the housing 40) to electronics (not shown) which are outside of the housing 40.

The housing 40 also contains the source of nitrite ions 26 or the medium 27. Any of the sources previously described may be used in this example device 200. The source of nitrite ions 26 or the medium 27 is contained within the housing 40 such that at least the working electrode mesh 12′ is in contact with the source of nitrite ions 26 or the medium 27.

In an example in which the source of nitrite ions 26 is used, electrochemical generation of nitric oxide using the planar patch 200 of FIG. 3 involves application of a cathodic voltage pulse to the working electrode mesh 12′ to clean the surface of the mesh 12′, and then application of an anodic voltage pulse to the working electrode mesh 12′ to produce a low concentration of Cu(I) ions at the mesh surface. The Cu(I) ions produced at the surface react directly with nitrite in the source of nitrite ions 26 to generate nitric oxide gas, which permeates through the housing 40 to the external environment. To observe consistent reduction of nitrite to NO, the two-step potential sequence (i.e., cathodic pulse followed by anodic pulse) is continuously and repeatedly applied to the working electrode mesh 12′.

In an example in which the medium 27 is used, electrochemical generation of nitric oxide using the planar patch 200 of FIG. 3 involves application of a cathodic voltage to the working electrode mesh 12′ to produce a low concentration of Cu(I)-ligand complex which reacts directly with nitrite in the solution 27 to generate nitric oxide gas, which permeates through the housing 40 to the external environment.

Referring now to FIG. 4A, an example of a gas delivery device 300 is depicted. This gas delivery device 300 includes a nitric oxide generating system 10 similar to that previously described in reference to FIG. 1A (except there is no outlet to an NO analyzer). It is to be understood that system 10′ shown in FIG. 1B may also be used in the system 300. The nitric oxide in the system 10 may be generated using any of the methods disclosed herein utilizing the source of nitrite ions 26 or the medium 27.

The gas delivery device 300 also includes an inlet conduit 49 for delivering oxygen gas (O₂) to the source of nitrite ions 26 or medium 27 in contact with the electrodes 12, 14. The inlet conduit 49 may be any suitable polymeric or other tubing attached to an oxygen gas generator (not shown).

The oxygen gas stream that is introduced into the system 10 picks up the nitric oxide that is generated in the source of nitrite ions 26 or the medium 27 as a result of the electrochemical method(s) disclosed herein. The resulting stream of oxygen gas and nitric oxide is then transported out of the system 10 through an outlet conduit 52. It is to be understood that this gas stream may include some contaminants. The outlet conduit 52 may be a tube that has low or no permeability to at least the oxygen gas and the nitric oxide. The length of the outlet conduit 52 may also be relatively short in order to avoid loss of gas before the stream is delivered to the oxygenator 51.

The stream is transported as a result of pressure from the oxygen gas generator (e.g., a compressed gas cylinder with a regulator to control the flow rate).

The outlet conduit 52 is configured to transport the stream of oxygen gas and nitric oxide (O₂+NO or NO+O₂) from the system 10 to an oxygenator 51, which includes membrane(s) 50 capable of filtering and cleaning the gas stream. In this particular example, the oxygenator 51 is a blood oxygenator, which includes a housing 53 with a blood inlet, a blood outlet, and a gas inlet.

The gas inlet of the housing 53 is operatively connected to the outlet conduit 52. More particularly, the gas inlet directs the stream of oxygen gas and nitric oxide from the outlet conduit 52 into membranes 50 that are contained within the housing 53. In this example, each membrane 50 is a hollow polymeric fiber having a first or interior surface I and a second or exterior surface E. A single blood oxygenator housing 53 may include thousands of hollow polymeric fibers. The stream of oxygen gas and nitric oxide is introduced adjacent to the first or interior surface I. The walls of the hollow polymer fibers act as filters, allowing only the oxygen gas and the nitric oxide from the stream to permeate therethrough (while trapping contaminants therein). As such, the cleaned stream of oxygen gas and nitric oxide exits from the second or exterior surface E into any blood contained within the housing 53 (as shown in the expanded portion of FIG. 4A).

The NO in this example serves to locally prevent platelet adhesion and activation on the second or exterior surface E of the membranes 50. The effect of the NO is localized since it reacts immediately with oxyhemoglobin to form met-hemoglobin. When the blood exits the oxygenator 51, NO is no longer present in the cleaned stream. As such, the blood, containing a cleaned stream of oxygen gas, can then exit the housing 53 and be delivered to a patient.

While one example of the gas delivery system 300 is depicted, it is to be understood that various other configurations may be utilized, for example, the blood oxygenator 51 may have a different design.

Referring now to FIG. 4B, another example of a gas delivery device 300′ is depicted. This gas delivery device 300′ also includes the nitric oxide generating system 10 similar to that previously described in reference to FIG. 1A (except there is no outlet to an NO analyzer). It is to be understood that system 10′ shown in FIG. 1B may also be used in the system 300′. The nitric oxide in the system 10 may be generated using any of the methods disclosed herein utilizing the source of nitrite ions 26 or the medium 27.

Similar to the gas delivery device 300, this device 300′ also includes the inlet conduit 49 for delivering oxygen gas (O₂) to the source of nitrite ions 26 or medium 27 in contact with the electrodes 12, 14, and the outlet conduit 52. As described above, the oxygen gas stream that is introduced into the system 10 picks up the nitric oxide that is generated in the source of nitrite ions 26 or the medium 27 as a result of the electrochemical method(s) disclosed herein. The resulting stream of oxygen gas and nitric oxide is then transported out of the system 10 through the outlet conduit 52 as discussed above.

The outlet conduit 52 is configured to transport the stream of oxygen gas and nitric oxide (O₂+NO or NO+O₂) from the system 10 to an oxygenator 51′, which includes a housing 53′ and a membrane(s) 50′ capable of filtering and cleaning the gas stream. In this particular example, the oxygenator 51 is part of an inhalation unit 56, which also includes a patient delivery system 54 to deliver the cleaned stream of oxygen gas and nitric oxide to a patient for the purpose of inhalation therapy.

A gas inlet of the housing 53′ is operatively connected to the outlet conduit 52. More particularly, the gas inlet directs the stream of oxygen gas and nitric oxide from the outlet conduit 52 towards the membrane 50′ that divides the housing 53′. In this example, the membrane 50 is a polymeric sheet having a first surface I and a second surface E. The stream of oxygen gas and nitric oxide is introduced adjacent to the first surface I. The membrane 50′ acts as a filter, allowing only the oxygen gas and the nitric oxide from the stream to permeate therethrough (while trapping contaminants in the one side 57 of the housing 53′). The cleaned stream of oxygen gas and nitric oxide exits from the second surface E.

In this example, the cleaned stream of oxygen gas and nitric oxide is delivered to a patient (e.g., for inhalation) through the patient delivery system 54 (which may include a tube and a respirator).

While one example of the gas delivery system 300′ is depicted, it is to be understood that various other configurations may be utilized. For example, a single polymer tube may form the inlet conduit 49 and the outlet conduit 52, and is positioned within the source 26 or medium 27 where NO is generated. In this example, the polymer tube would be permeable to the NO, and the stream of oxygen gas or air transported through the tube would pick up the NO through the permeable tube (i.e., NO would diffuse through the polymer tubing and join the gas stream). The polymer tube could be configured to deliver the stream (including oxygen gas and nitric oxide) directly to the patient. The polymer tube may include a membrane 51′ so that contaminants are not delivered to the patient.

The NO generation methods described herein may be controlled to selectively generate NO at a desired time. For example, control of the potential applied to the working electrode 12 can turn on the generation of NO or can turn off the generation of NO. For efficient bactericidal activity, it may be desirable to turn NO generation on and off at least once a day, where the on cycle ranges from about 1 hour to about 2 hours or about 3 hours. In some instances, it may also be desirable to turn NO generation on and off multiple times within a day. In other examples, the device may be configured to sense the presence and/or absence of bacteria and, in response, turn on and/or off NO generation, respectively. The flux of NO that is generated may also be modulated by altering an amount of a surface area of the working electrode 12 or mesh 12′ that is exposed to the source of nitrite ions 26 or the medium 27 (e.g., changing the length of the electrode 12 or mesh 12′), by altering a concentration of nitrite in the source of nitrite ions 26 or by altering a concentration of nitrite and/or Cu(II)-ligand complex in the medium 27, by altering a magnitude of the cathodic voltage (e.g., a more negative voltage for a short time followed by a less negative voltage for a longer time) and/or the anodic voltage, by altering the pH, and/or by altering the concentration of additive(s) that are included.

In the examples disclosed herein, the NO generation may take place in air.

To further illustrate the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the present disclosure.

EXAMPLES Example 1

A silicone rubber tubing (2 cm length, 0.51 mm inner diameter, and 0.94 mm outer diameter) was sealed at one end with silicone rubber sealant. A 2 cm long polytetrafluoroethylene (PTFE)-coated silver/silver chloride wire was used as the reference electrode, and a 2 cm long PTFE-coated copper wire was used as the working electrode. The bare copper wire had an outer diameter of 0.127 mm, and coated copper wire had an outer diameter of 0.152 mm. The PTFE was removed from the ends of the silver/silver chloride wire and the copper wire in 20 mm and 10 mm lengths, respectively. The exposed ends of the respective wires were coiled separately. The coiled ends were inserted into the silicone rubber tubing so that the silver/silver chloride wire and the copper wire were not in direct metallic connection.

A source of nitrite was loaded into the tubing. The source of nitrite included 1 M NaNO₂, 0.138 M NaCl, 0.02 M EDTA in 1 M phosphate buffered saline (PBS). The pH was adjusted to 6.8 with NaOH or using appropriate ratios of phosphate salts.

The silicone rubber tubing was then sealed to form a catheter. PTFE-coated silver/silver chloride wire and PTFE-coated copper wire extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

A cathodic voltage (−0.7 V vs. NHE) was applied to the working electrode for about 3 minutes, and then an anodic voltage (+0.2 V vs. NHE) was applied to the working electrode for about 3 minutes. The pulse sequence was initiated for 1 hour every 2 hours over a 24 hour period. The NO flux from the surface of the silicone rubber tubing is shown in FIG. 5A. One 2 hour segment of FIG. 5A is shown expanded in FIG. 5B. The left hand side of the graph illustrates when the voltage cycle is turned off, and the right hand side of the graph illustrates when the voltage cycle is turned on.

As illustrated in FIG. 5B, a catheter with a 2 cm long thin copper electrode was able to generate an average NO flux of 0.6×10⁻¹⁰ mol·cm⁻²·min⁻¹ when the previously described voltage cycle was implemented. In the absence of any voltage, nitric oxide was not generated and thus the NO flux was zero. It is noted that the average flux reported in this Example is based upon the surface area of the entire silicon rubber tubing, not the copper electrode alone. The results shown in FIG. 5A illustrate that the potential applied to the copper coated electrode can be controlled to turn on or off the release of NO through the walls of the silicone rubber tubing. The silicone rubber tubing provided a barrier against the leaching of nitrite from the catheter, but also allowed for the electrochemically generated NO gas to readily diffuse out of the catheter.

Example 2

A bacterial biofilm prevention study was performed using the NO generating catheters of Example 1. Two strains of bacteria were used, namely E. coli and A. baumannii.

The experiment was performed over a 1 week period with continuous flow of media using a Center for Disease Control (CDC) bioreactor. 4 NO generating catheters were immersed in the media containing either E. coli or A. baumannii. Two of the catheters were connected to an amperometric work station and a continuous potential program was applied to the respective working electrodes. The potential program included 3 minutes at −0.97 V vs. Ag/AgCl (−0.7 V vs. normal hydrogen electrode) for reduction, and −0.07 V vs. Ag/AgCl (+0.2 V vs. normal hydrogen electrode) for liberation of NO. The other two catheters were used as controls. These control catheters contained the same nitrite salt solution and wires, but were not linked to potentiostats.

At the end of the one week period, the catheters were stained with fluorescent dyes (SYTO-9 and propidium iodide) for 20 minutes in the dark. The catheters were put on a glass slide before being observed with a fluorescence microscope equipped with Fluorescent Illumination System (X-cite 120, EXFO) and appropriate filter sets. FIGS. 6A and 6B illustrate the bacterium counting results after 7 days. These results are based upon the staining and fluorescence imaging discussed above. The bacterium counting results show that the NO generating catheters that released NO had 90% less viable E. coli on their surfaces, and had 98% less viable A. baumannii on their surfaces, when compared to the control catheters (which did not release NO).

Example 3

A silicone rubber tubing (2 cm length, 0.51 mm inner diameter, and 0.94 mm outer diameter) was sealed at one end with silicone rubber sealant. A 2 cm long polytetrafluoroethylene (PTFE)-coated silver/silver chloride wire was used as the reference electrode, and a 2 cm long PTFE-coated copper wire was used as the working electrode. The bare copper wire had an outer diameter of 0.127 mm, and coated copper wire had an outer diameter of 0.152 mm. The PTFE was removed from the ends of the silver/silver chloride wire and the copper wire in 20 mm and 10 mm lengths, respectively. The exposed ends of the respective wires were coiled separately. The coiled ends were inserted into the silicone rubber tubing so that the silver/silver chloride wire and the copper wire were not in direct metallic connection.

A source of nitrite was loaded into the tubing. The source of nitrite included 1 M NaNO₂, 0.138 M NaCl, 25 mM EDTA in 1 M phosphate buffered saline (PBS). The pH was adjusted to 7.2 with NaOH or using appropriate ratios of phosphate salts.

The silicone rubber tubing was then sealed to form a catheter. PTFE-coated silver/silver chloride wire and PTFE-coated copper wire extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

A cathodic voltage (−1.2 V vs. NHE) was applied to the working electrode for about 30 seconds, and then an anodic voltage (+0.2 V vs. NHE) was applied to the working electrode for about 30 seconds. The pulse sequence was performed over a 14 hour period. The pulse sequence was initiated for about 2 hours at hours 0, 7 and 12, and for about 5 hours from hour 3 to hour 8. The NO flux from the surface of the silicone rubber tubing is shown in FIG. 7. The results shown in FIG. 7 illustrate that the potential applied to the copper coated electrode can be controlled to turn on or off the release of NO through the walls of the silicone rubber tubing. The silicone rubber tubing provides a barrier against the leaching of nitrite from the catheter, but also allows for the electrochemically generated NO gas to readily diffuse out of the catheter.

Example 4

A bacterial biofilm dispersal study was performed using four NO generating catheters and one strain of bacteria, namely E. coli.

For each catheter, a silicone rubber tubing (2 cm length, 0.51 mm inner diameter, and 0.94 mm outer diameter) was sealed at one end with silicone rubber sealant. A 2 cm long polytetrafluoroethylene (PTFE)-coated silver/silver chloride wire was used as the reference electrode, and a 2 cm long PTFE-coated copper wire was used as the working electrode. The bare silver/silver chloride wire had an outer diameter of 0.125 mm, and the coated silver/silver chloride wire had an outer diameter of 0.176 mm. The bare copper wire had an outer diameter of 0.127 mm, and the coated copper wire had an outer diameter of 0.152 mm. The PTFE was removed from the ends of the silver/silver chloride wire and the copper wire in 20 mm lengths to expose the bare electrodes. The exposed ends of the respective wires were coiled separately. The coiled ends were inserted into the silicone rubber tubing so that the silver/silver chloride wire and the copper wire were not in direct metallic connection.

A source of nitrite was loaded into the tubing. The source of nitrite included 1 M NaNO₂, 0.138 M NaCl, 0.02 M EDTA in 1 M phosphate buffered saline (PBS). The pH was adjusted to 6.8 with NaOH or using appropriate ratios of phosphate salts.

The silicone rubber tubing was then sealed to form the catheter. PTFE-coated silver/silver chloride wire and PTFE-coated copper wire extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

The experiment was performed over a 2 day period with continuous flow of media (80 mL/hr) using a drip-flow bioreactor. The catheters were immersed in the media containing E. coli. Two of the catheters were connected to a potentiostat and a pulse sequence was applied to the respective working electrodes for 3 hours after two days in the flowing media with the cells without generating NO. These catheters are referred to as the NO releasing catheters. One cycle of the pulse sequence included 30 seconds at −1.2 V vs. Ag/AgCl wire, and 30 seconds at +0.2 V vs. Ag/AgCl wire. These NO releasing catheters were able to generate an average NO flux of 1.2*10⁻¹⁰ mol/cm²*min when this pulse sequence was applied. The other two catheters were used as controls. These control catheters contained the same nitrite salt solution and wires, but were not connected to potentiostats.

At the end of the 2 day period, one NO generating catheter and one control catheter were used for detection of viable bacteria on the catheter surfaces by a plate counting method. The other NO generating and control catheters were used for imaging. In particular, these two catheters were stained with fluorescent dyes (SYTO-9 and propidium iodide) for 20 minutes in the dark. The catheters were put on a glass slide before being observed with a fluorescence microscope equipped with Fluorescent Illumination System (X-cite 120, EXFO) and appropriate filter sets.

FIG. 8A illustrates the results observed for the one control catheter and the one NO releasing catheter obtained by the fluorescence imaging of total bacteria on the respective surfaces. As shown in FIG. 8A, the fluorescent imaging experiments indicate a dramatic reduction in number of cells left on the surface for the NO releasing catheter.

FIG. 8B illustrates the bacterium counting results (Colony Forming Units, CFU) after 2 days for the other control catheter and the other NO releasing catheter. The bacterium counting results (FIG. 8B) illustrate that NO generating catheters that were turned on for only 3 hours of NO release had nearly a 3 log unit reduction in the number of living E coli cells on their surface compared to the control.

Both the fluorescence imaging and the bacterium counting results demonstrate the effectiveness of using the electrochemically modulated NO release catheter to disperse bacteria biofilm after they have formed on the surface. In particular, the results indicate the effectiveness using a one-time application of the NO release cycle for a relatively short period of time.

Example 5

A surface of a silicone rubber tubing (0.541 μm inner diameter, and 940 μm outer diameter) was modified by impregnating the tubing with tetradodecylammonium tetrakis (4-chlorophenyl) borate (ETH 500) and dioctyl sebacate (DOS) in an m-xylene solution. Impregnation was allowed to take place for 24 hours, and then the tubing was air-dried overnight inside of a fume-hood. The dried tubing was then put in an oven of 120° C. for about 1 hour.

A source of nitrite was loaded into the tubing. The source of nitrite included 1 M NaNO₂, 0.138 M NaCl, 20 mM EDTA in 1 M phosphate buffered saline (PBS).

Two cm long of 127 μm PTFE-coated copper and PTFE-coated Ag/AgCl wires were then inserted inside the tube containing the source of nitrite. The tube was sealed at the open end with a silicone sealant and was cured overnight at room temperature. A portion of each of the wires extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

The control catheter was the same type of surface modified catheter with the same source of nitrite and the same electrodes inserted inside the tubing, but the NO release was never electrochemically initiated.

The catheter and control catheter put inside respective drift flow bioreactors to grow biofilm on the respective surfaces. A standard or double junction commercial Ag/AgCl reference electrode was also placed inside the same channel with the catheter, and with the control catheter. 10% live bacteria was then passed through the respective channels. The background open circuit potential (BOCP) was measured for 30 minutes vs. the respective external Ag/AgCl reference electrode. The chambers were then inoculated with E. Coli bacteria for one hour and then the media was flowed through continuously again. The open circuit potential (OCP) measurement against the external Ag/AgCl reference electrode was recorded every hour.

For the sample including the catheter, when the change of 170 mV in OCP was observed from baseline (see FIG. 9), an electrochemical pulse was turned on to release NO for 2 hours. The electrochemical pulse used was −1.2 V for 30 seconds and +0.2 V for 30 seconds. The NO flux used for the first NO release was 1×10⁻¹⁰ moles/cm²·min. The OCP was measured again after stopping the electrochemical pulse.

The OCP was again measured every hour until the next event (i.e., a change in OCP) was observed. This indicated that bacteria were again starting to stick on the catheter surface. The electrochemical pulse was again turned on to release NO for 2 hours. The NO flux used for the second NO release was 0.5×10⁻¹⁰ moles/cm²·min. The electrochemical pulse used was −1.2V for 30 seconds and +0.1 for 30 seconds.

After the experiment, the catheter and the control catheter were taken out of the respective chambers and the surface bacteria were dispersed into respective solutions via a homogenizer. The solutions were plate counted to determine the number of live bacteria left on the catheter surface and the control catheter surface. The number of bacteria after the experiment with the catheter was found to be 36% less than the control.

Example 6

Five example catheters (S1-S5) and four control catheters (C1-C4) were prepared to assess the in vivo effects of the pulsed electrochemical release of NO on thrombus formation. All of the example catheters and the control catheters were prepared as previously described in Example 3, except an additional length (about 3 inches) of inert tubing was attached to the top end to enable insertion of the distal tips into rabbit veins.

White rabbits (2.5-3.5 kg, Myrtle's Rabbitry, Thompson's Station, Tenn.) were used for the thrombus experiment. Intramuscular injections of 5 mg/kg xylazine injectable (AnaSed Lloyd Laboratories Shenandoah, Iowa) and 30 mg/kg ketamine hydrochloride (Hospira, Inc. Lake Forest, Ill.) were used to induce anesthesia before each rabbit experiment. Maintenance anesthesia was administered via a diluted intravenous (IV) infusion of ketamine (2 mg/ml) at a rate of 1.53 mg/kg/h. IV fluids of Lactated Ringer's were given at a rate of 33 ml/kg/h to maintain blood pressure stability.

Example catheters S1, S3, S4 and S5 and control catheters C1-C4 were implanted in rabbit jugular veins and allowed to remain in the veins for 6 hours. Example catheter S2 was implanted into a rabbit leg vein and was allowed to remain for 6 hours. For each of the Example catheters, an electrochemical pulse sequence was turned on, with the NO flux ranging from 0.8*10⁻¹⁰ moles/cm²·min to 1.1*10⁻¹⁰ moles/cm²·min to release NO. The particular NO flux at 37° C. for the respective Example catheters is shown in Table 1. For the control catheters, the electrochemical pulse sequence was turned off, with the NO flux<<0.3*10⁻¹⁰ moles/cm²·min.

After the 6 hours, the example and control catheters were explanted and thrombus on each example and control catheter was recorded via digital photography. Red pixels were counted from the photo using Image J software. The surface coverage was calculated using the red pixel data, and these results are shown in Table 1.

TABLE 1 Thrombus Total Sample or Area/ Area/ Surface Control NO flux @ 37° C. cm² cm² Coverage S1 ~1.1 *10⁻¹⁰ moles/cm² · min 0.021 0.315 6.7% S2 ~1.0 *10⁻¹⁰ moles/cm² · min 0.010 0.202 5.0% S3 ~1.1 *10⁻¹⁰ moles/cm² · min 0.039 0.202 19.3% S4 ~0.8 *10⁻¹⁰ moles/cm² · min 0.078 0.167 46.7% S5 ~0.9 *10⁻¹⁰ moles/cm² · min 0.083 0.252 46.7% AVG. 22.12% C1 N/A 0.214 0.380 56.3% C2 N/A 0.263 0.360 73.1% C3 N/A 0.690 1.107 62.4% C4 N/A 0.165 0.273 60.2% AVG. 63.0% As illustrated, each of the example catheters had less thrombus formation than each of the control catheters. For those example catheters when the NO flux was lower, there was a bit more thrombus formation. Overall, these results illustrate that in vivo electrochemical generation of NO reduces thrombus formation.

A similar experiment was performed using an example catheter and a control catheter (as previously described), except that both of the catheters were allowed to remain in the jugular veins for 8 hours. An electrochemical pulse sequence was turned on using the example catheter, but was not turned on for the control catheter. Upon extraction of the example catheter and the control catheter from the rabbit veins, digital photographs were taken. These photographs are schematically represented in FIGS. 10A and 10B. As depicted, the example catheter used to electrochemically generate NO in vivo had very little thrombus formation, as opposed to the control catheter, which was almost completely covered with thrombus.

Example 7

A three electrode system similar to that shown in FIG. 1B was used in this example. A 0.0314 cm² gold disc electrode was used as the working electrode, a platinum coil was used as the counter electrode, and a silver/silver chloride electrode was used as the reference electrode. The bulk solution included 1 mM CuTPMA in 0.1 M MOPS buffer (pH 7.2) with different levels of nitrite in N₂ (i.e., 0 mM nitrite, 1 mM nitrite, 10 mM nitrite, and 100 mM nitrite).

Cyclic voltammetry (CV) was performed with a scan rate of 50 mV/s, and the results are shown in FIG. 11. The reversible peaks in the absence of nitrite correspond to a one electron reduction from Cu(II) to Cu(I), and the characteristic catalytic peak in the presence of nitrite indicates the nitrite is catalytically reduced.

Similar CV experiments were performed with a 0.0314 cm² Pt disc electrode and a 0.0707 cm² glassy carbon disc electrode. The bulk solutions in these experiments included 1 mM CuTPMA in 0.1 M MOPS buffer (pH 7.2) with different levels of nitrite in N₂ (i.e., 0 mM nitrite, 10 mM nitrite, and 100 mM nitrite). While not shown, the CV for each of these experiments was similar to the CV shown in FIG. 11.

Example 8

A three electrode system similar to that shown in FIG. 1B was used in this example. A 0.071 cm² in surface area glassy carbon electrode was used as the working electrode, a platinum coil was used as the counter electrode, and a silver/silver chloride electrode was used as the reference electrode. The bulk solution included 4 mM CuTPMA and 100 mM nitrite in 0.1 M MOPS buffer (pH 7.2).

A cathodic voltage was applied to the bulk solution and was modulated over time. As shown in FIG. 12, low, medium, and high flux of constant NO release can be modulated by applying −0.2 V, −0.3 V, and −0.4V respectively (vs. 3M Ag/AgCl reference electrode) in the bulk solution. In this example, the NO formed was electrochemically detected by a chemiluminescence nitric oxide analyzer (NOA).

Example 9

A single lumen silicone rubber tubing (7.5 cm length, inner diameter 1.47 cm, and outer diameter 1.96 cm) was sealed at one end with silicone rubber sealant. A polytetrafluoroethylene (PTFE)-coated silver/silver chloride wire (with 0.039 cm² surface area exposed) was used as the reference electrode, and a PTFE-coated platinum wire (with 0.079 cm² surface area exposed) was used as the working electrode. The exposed ends of the respective wires were coiled separately. The coiled ends were inserted into the single lumen silicone rubber tubing so that the silver/silver chloride wire and the copper wire were not in direct metallic connection.

A solution was loaded into the single lumen silicone rubber tubing. The solution included 2 mM CuTPMA, 0.4 M NaNO₂, and 0.2 M NaCl in 0.5 M MOPS buffer (pH 7.2).

The silicone rubber tubing was then sealed to form a catheter. PTFE-coated silver/silver chloride wire and PTFE-coated copper wire extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

A dual lumen catheter was also prepared in a similar manner by introducing the solution and electrodes into one of the two lumens (where the dedicated NO generating lumen is slightly larger than the open lumen for blood of infusing agents).

A −0.4 V vs. Ag/AgCl voltage was applied to the platinum electrode of the single lumen catheter for 8 days, although there were some instances at which the voltage was turned off. When the voltage was turned off at days 1, 2, 5, 6, and 7, the NO generation significantly decreased. The results are shown in FIGS. 13A through 13H. As illustrated over these figures, the NO flux can be modulated by turning the voltage on and off, but when on, a relatively constant NO flux can be achieved.

Example 10

A single lumen silicone rubber tubing (7.5 cm length, inner diameter 1.47 cm, and outer diameter 1.96 cm) was sealed at one end with silicone rubber sealant. A polytetrafluoroethylene (PTFE)-coated silver/silver chloride wire (with 0.039 cm² surface area exposed) was used as the reference electrode, and a PTFE-coated platinum wire (with 0.080 cm² surface area exposed) was used as the working electrode. The exposed ends of the respective wires were coiled separately. The coiled ends were inserted into the single lumen silicone rubber tubing so that the silver/silver chloride wire and the copper wire were not in direct metallic connection.

A solution was loaded into the single lumen silicone rubber tubing. The solution included 4 mM CuTPMA, 0.4 M NaNO₂, and 0.2 M NaCl in 0.5 M MOPS buffer (pH 7.2).

The silicone rubber tubing was then sealed to form a catheter. PTFE-coated silver/silver chloride wire and PTFE-coated copper wire extended out of the silicone rubber tubing as respective leads to the reference and working electrodes.

A dual lumen catheter may be formed in a similar manner by introducing the solution and electrode into one of the two lumens.

The cathodic voltage (vs. 0.2 M Cl⁻Ag/AgCl) was applied to the platinum electrode of the single lumen catheter for about 12 hours. The voltage was modified over this time period to illustrate the effect on the modulation of NO flux. The results are shown in FIG. 14. As illustrated, the NO flux can be modulated by applying different voltages, and in this particular example, the flux can vary from about 0.05 to about 3.25×10⁻¹⁰ mol min⁻¹ cm⁻².

Example 11

The single and dual lumen catheters of Example 9 were used in 7 hour in vivo testing to determine the efficacy of examples of the method disclosed herein using the medium 27.

Two of the single or dual lumen catheters were placed in rabbit jugular veins (n=3 rabbits) with one of the catheters “turned on” (−0.5 V) and the other “turned-off” (not linked to potentiostat, i.e., the control). The degree of thrombus was assessed by imaging the catheters after removal. Red pixels were counted from the photo using Image J software. The surface coverage was calculated using the red pixel data. The results are shown in FIG. 15. The NO release catheters consistently exhibited reduced thrombosis, with an average 89% reduction in thrombus area for the single lumen catheters when compared with the control catheters. The in vivo thrombosis experiments for the dual lumen catheters showed that the NO release catheters had an average reduction of 69% in thrombus area when compared with the control catheters.

The dual lumen catheters were asymmetric (where the dedicated NO generating lumen is slightly larger than the open lumen for blood of infusing agents). Although the asymmetry could have caused an uneven distribution of NO at the outer and inner surfaces of the lumens, the silicone rubber material had a very high NO solubility and mobility. This material provided a reservoir for the generated NO and the improved distribution of the gas. This was confirmed by finite element analysis (COMOSOL Multiphysics), as similar NO concentration was found near the surfaces of the two respective lumens (see FIGS. 16A and 17B).

FIG. 16A shows the finite element analysis simulation results after 2 hours of electrochemically generating NO from electrodes placed in the right side lumen. The grey scale code shows the concentration of NO at different locations within the catheter lumens, within the polymer walls, and within the adjacent solution. The highest concentrations are within the walls of the tubing, due, at least in part, to the high partition coefficient for NO to solubilize in the silicone rubber material. This high solubility enables there to be a relatively low asymmetry in the concentrations of NO that exist in the solution phase on both sides of the dual lumen catheter. FIG. 16B shows the actual relative concentrations going from left to right across the width of the catheter (i.e., across the line shown through the dual lumen catheter in FIG. 16A), starting in solution phase on the left side of the catheter. The highest levels are within the walls of the tubing, with the highest within the thin silicone wall between the two lumens of the catheter. It is noted in FIG. 16B, that the concentration values on the Y-axis are multiple by 10⁻⁵ (as shown at the top of the Y-axis).

Example 12

To assess the antimicrobial activity of the dual lumen catheters of Example 9, the amount of surface-adhered bacteria was determined after a highly inoculated media solution containing the microbes as flowed continuously over the surface of the catheters for several days. The dual lumen catheters were tested in a drip flow system, which mimicked the catheter environment in vivo. E. coli were grown on the catheters with continuous nutrient flowing for 3 days and the NO release was turned on for only 3 hours each day with a flux of 0.6×10⁻¹⁰ mol min⁻¹ cm⁻².

The results are shown in FIGS. 17A and 17B. Even with the relatively low amount of periodic NO release, the plate counts showed a more than 1000-fold decrease of viable bacteria on the channel surface in which the NO releasing catheters (n=5) were placed. The reduction of biofilm formation on the channel walls was so great that it could even be observed visually without a microscope. In addition, more than 100-fold decrease in viable bacteria was observed on the catheter surfaces with NO release turned on periodically.

Example 13

When the medium 27 is used in some of the examples disclosed herein, a competing reaction of oxygen with reduced Cu(I)TPMA may take place. The effect of oxygen was tested in this example. Cyclic voltammetry (CV) was performed with a scan rate of 50 mV/s using a bulk solution including 1 mM CuTPMA in 0.1 M MOPS buffer (pH 7.2) with different levels of nitrite in air (i.e., 0 mM nitrite, 1 mM nitrite, 10 mM nitrite, and 100 mM nitrite). A 2 mm gold disc working electrode and a Ag/AgCl reference electrode were used.

The results are shown in FIG. 18. The CV is similar in the presence and absence of oxygen, suggesting no significant effect (i.e., does not significantly suppress NO production).

Example 14

It is believed that the Cu(II)-ligand complex cannot transport through PDMS to any significant degree. A 7 day copper leaching test was performed, and the results confirmed this belief. Catheters of Example 9 were placed in PBS buffer at room temperature for 7 days. No copper was detected in the soaking solution by ICP-OES.

Example 15

The effect of nitrite level in the initial medium 27 on N₂O production was tested.

A calibration method was used for quantification of N₂O. First, standard N₂O solutions (i.e., 0.25 mM, 1 mM, 2 mM, and 2.5 mM N₂O) were prepared by adding different amounts of saturated N₂O solution to an airtight glass containing 10 mL of MOPS buffer which had been deaerated by purging Ar for 30 minutes. The headspace N₂O was then transferred into a vacuumed gas phase IR cell using a cannula, and was analyzed using a Perkin-Elmer FT-IR. A calibration curve was obtained by integration of the N₂O feature peaks at 2235 cm⁻¹ and 2212 cm⁻¹. These IR spectra of N₂O standards are shown in FIG. 19A and the corresponding calibration curve is shown in FIG. 19B.

For the bulk electrolysis experiment, an airtight glass cell containing 10 mL of different levels of nitrite (50, 100, 200 and 400 mM) in 2 mM CuTPMA, 0.2 M NaCl and 0.5 M MOPS buffer (pH 7.2) was used. The solutions were first purged with Ar for 30 minutes before each experiment. A Pt wire electrode (0.32 cm²) was used as the working electrode and Ag/AgCl wire was used as the reference/counter electrode. A constant potential (−0.4 V vs. 0.2 M Ag/AgCl) was applied for 3 hours with stirring, after which the headspace gas was transferred into a vacuumed gas phase IR cell using a cannula, and was analyzed using a Perkin-Elmer FT-IR. These results are shown in FIG. 19C. As depicted, as the level of nitrite was increased, the level of N₂O that was produced decreased dramatically.

As illustrated in these examples, nitric oxide gas can be efficiently generated from a source of nitrite ions 26 or a medium 27 (including the Cu(II)-ligand complex) using electrodes and, respectively, the two-step voltage cycle or the application of a constant cathodic voltage. In some examples, the reductive cleaning of the electrode prepares the electrode for anodic liberation of Cu(I) ions, which react with nitrite to generate NO. It is believed that the processes disclosed herein can be employed to modulate the release of NO from polymer surfaces used to prepare, for example, in-dwelling catheters. Since continuous fluxes of NO to kill or disperse biofilm forming on microbes or to prevent platelet induced clotting may not be necessary, it is believed that catheters and other medical devices disclosed herein may be utilized effectively for longer periods of time with a given supply of nitrite. This is due, at least in part, to the ability to turn the NO release on and off. It is further believed that when NO is produced at high enough levels in pulses at a defined frequency, the total moles of NO required for delivery over a given time period will be much less than the total moles of NO required with continuous release NO donor chemistry.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from about 1 cm to about 2 cm should be interpreted to include not only the explicitly recited limits of about 1 cm to about 2 cm, but also to include individual values, such as 1.5 cm, 1.75 cm, etc., and sub-ranges, such as from about 1.25 cm to about 1.75 cm, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/−5%) from the stated value. When applied potential values are discussed, it is to be understood that wider ranges may be suitable. In some of the examples disclosed herein, increasing the magnitude of the anodic potential pulse increases the amount of Cu(I), and thus also increases the amount of NO generated. In other of the examples disclosed herein, increasing the magnitude of the cathodic potential pulse (i.e., a more negative cathodic potential) increases the amount of Cu(I)-ligand complex that is generated, and thus also increases the amount of NO generated. As such, it is believed that a broad range is applicable for the applied potential values, the limits of which may depend on the desired amount of Cu(I) species and NO to be generated, or on the time required to clean the working electrode.

Furthermore, reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting. 

What is claimed is:
 1. A method for generating nitric oxide, comprising: providing a medium including a Cu(II)-ligand complex and an excess of a source of nitrite ions; and applying a cathodic voltage to a working electrode positioned in contact with the medium, thereby reducing the Cu(II)-ligand complex to a Cu(I)-ligand complex which reacts with some nitrite from the source of nitrite ions to form the nitric oxide, wherein the nitric oxide is not bound to the Cu(I)-ligand complex and wherein excess nitrite is bound to the Cu(I)-ligand complex.
 2. The method as defined in claim 1, further comprising modulating a flux of the generated nitric oxide by any of altering an amount of a surface area of the working electrode that is exposed to the medium, or altering a concentration of any of the Cu(II)-ligand complex or the source of nitrite ions in the medium, or altering a magnitude of the cathodic voltage over time.
 3. The method as defined in claim 1 wherein the applying of the cathodic voltage is accomplished at predetermined intervals.
 4. The method as defined in claim 1 wherein the applying of the cathodic voltage includes: applying a first cathodic voltage to increase NO production for a predetermined time period; and then applying a second cathodic voltage that is less negative than the first cathodic voltage to decrease NO production after the predetermined time period has expired.
 5. The method as defined in claim 1, further comprising transporting the nitric oxide out of the medium without performing additional steps to oxidize the ligand complex.
 6. The method as defined in claim 1, further comprising: introducing an oxygen gas stream into the medium, whereby the oxygen gas stream picks up the nitric oxide; and transporting the oxygen gas stream including the nitric oxide out of the medium.
 7. The method as defined in claim 1 wherein the Cu(II)-ligand complex is selected from the group consisting of Cu(II)-tri(2-pyridylmethyl)amine, Cu(II)-tri(2-dimethylamino)ethyl]amine, Cu(II)-tri(2-pyridylmethyl)phosphine, and combinations thereof.
 8. The method as defined in claim 1 wherein the medium includes at least 100 mM of the source of nitrite ions. 